The present invention relates to wireless telecommunication systems. More particularly, and not by way of limitation, the invention is directed to a method of supporting frequency-selective repeaters in a wireless telecommunication system.
The following acronyms are used in the description herein:
3GPP Third Generation Partnership Project
BS Base Station
CQI Channel Quality Indicator
DL Downlink
DoA Direction of Arrival
E-UTRAN Evolved UMTS Radio Access Network
FDMA Frequency Division Multiple Access
FS Frequency-Selective
LTE Long Term Evolution
MAC Medium Access Control
MME Mobility Management Entity
OFDM Orthogonal Frequency Division Multiplexed
OFDMA Orthogonal Frequency Division Multiple Access
PDCCH Physical Downlink Control Channel
PH Power Headroom
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
RACH Random Access Channel
RB Resource Block
RS Reference Signals
RSRP Reference Signal Received Power
RSRQ Reference Signal Received Quality
Rt_BS Uplink Received Signal Strength Threshold at Base Station
Rx Uplink Received Signal Strength
RTT Round Trip Time
SAE System Architecture Evolution
S-GW Serving Gateway
SRS Sounding Reference Signal
UE User Equipment
UMTS Universal Mobile Telecommunication System
X2 Interface between eNodeBs
Un Interface between eNodeB and eNodeR (formerly X3)
In 3GPP, work is ongoing on the Long Term Evolution (LTE)-Advanced effort. In the LTE-Advanced network, relays will be used to enhance coverage and increase data rate in cell borders without increasing the number of conventional base station (BS) sites. Layer 1 relays, also referred to as advanced repeaters, are one of the potential technology components of LTE-Advanced. The main difference between an advanced repeater and a conventional repeater is that the advanced repeater includes one or several advanced functions, such as advanced antenna processing and/or frequency-selective (FS) amplification. Despite the use of advanced functions, repeaters are considered to be simpler than L2/L3 relays, since the data signal is not detected and decoded but only amplified and forwarded.
FIG. 1 is an illustrative drawing showing the basic principle of conventional FS repeater operation. It is assumed in this illustration that UEs are scheduled such that each user occupies a part of the entire bandwidth. Among these UEs, UE1 and UE2 are associated with the same repeater and others are not associated with this repeater. If the repeater is a conventional repeater, it amplifies the entire bandwidth regardless of how the users are scheduled. If the repeater is an FS repeater, it only amplifies the resource blocks (RBs) allocated to UE1 and UE2. FS repeaters are particularly beneficial in Frequency Division Multiple Access (FDMA) systems—e.g. Orthogonal Frequency Division Multiple Access (OFDMA)—where typically only part of the cell bandwidth (a sub-set of the resource blocks) is used by one UE at a time. The repeater can only amplify this part of the allocated bandwidth provided that an association exists between the UE and the repeater.
In LTE and LTE-Advanced networks, scheduling is modeled in the Medium Access Control (MAC) layer and is performed by a scheduler residing in the radio network node such as base station or eNodeB or Node B. The scheduler assigns RBs for the downlink (assignments) as well as for the uplink (grants) and transmits them together with a UE identifier using the downlink control channel such as the Physical Downlink Control Channel (PDCCH). To assist downlink scheduling decisions in the eNodeB, the mobile terminal or User Equipment (UE) can be configured to transmit downlink channel state information (CSI) such as Channel Quality Indicator (CQI) reports on a configured uplink control channel or resource such as the Physical Uplink Control Channel (PUCCH) or on a dedicated or shared channel or resource such as the Physical Uplink Shared Channel (PUSCH). CQI reports are typically based on some sort of downlink pilot or reference signal such as a downlink common reference signal (CRS). The uplink channel-dependent scheduling is typically based on the quality measured by the eNode B on some sort of uplink pilot or reference signal such as Sounding Reference Signals (SRS). The scheduler uses the reported CQI information to perform fast channel dependent link adaptation and to change allocations in the time and frequency domains.
Repeaters can get the assignments and grants by listening to the downlink control channel such as the PDCCH. In general, an FS repeater would be required to listen to any control channel that carries scheduling information. Besides acquiring the scheduling information, the UE-repeater association relationships are needed in order for the FS repeater to work properly. A repeater that is associated with a particular UE only amplifies the signals transmitted towards the associated UE or from the associated UE to the base station.
There are three known alternatives for establishing the UE-repeater association relationships:                Alternative 1: UEs measure on the reference signal (RS) from both the eNodeB and the repeater and report the measurements to the eNodeB. Based on these reports, the eNodeB establishes an association relationship between a UE and a repeater. An underlying assumption is that repeaters transmit their own reference signals to enable downlink measurements to be identified.        Alternative 2: UEs transmit UL channel soundings. Repeaters measure the channel soundings and report the measurements to the eNodeB. The eNodeB uses the reports to establish the UE-repeater association.        Alternative 3: An implicit association is made using traditional measurements such as the Channel Quality Indicator (CQI) and/or neighbor cell measurements (for example, RSRP, RSRQ, and the like). Repeaters simply amplify and forward these reported measurements to the eNodeB, which uses these reported measurements to establish the UE-repeater association.        